Conventionally, a refrigeration system, as proposed in U.S. Pat. No. 2,299,811, is well-known, which is so constructed that a rotary compressor is used which has a cylinder having a suction port and discharge port, with an injection pressure port opening at a pumping chamber between the ports. A refrigeration pipe line system connecting the suction port and discharge port is provided with a heat exchanger, two-divided expansion mechanisms, and a gas-liquid separator interposed at an intermediate portion between the expansion mechanism. A gas injection passage tube connects with a gas zone of the gas-liquid separator and communicates with the injection pressure port so that an injection pressure gas refrigerant separated by the gas-liquid separator is injected into the pumping chamber at the cylinder to increase the capacity of the compressor above the rated capacity to thereby achieve a capacity increases for the refrigeration system.
Another refrigeration system has been proposed, which is provided with a by-pass passage channel through which the injection pressure port communicates with the suction port at the previously described compressor, and solenoid open-close valves are provided at the by-pass passage channel and injection passage channel respectively, so that each valve is switched to inject the injection pressure gas refrigerant separated by the gas-liquid separator, from the injection pressure port into the pumping chamber, thereby raising the capacity of the refrigeration system alternatively, a part of the gas refrigerant taken up from the suction port to the pumping chamber is by-passed toward the suction port, so that the effective volume of the pumping chamber is reduced, thereby reducing the refrigeration system capacity.
The refrigeration system switches the open-close valve to enable a desirably selective decrease or increase in capacity. The injection pressure port is used in both cases for injecting an injection pressure gas refrigerant and for by-passing a part of the drawn-in gas refrigerant. Also, the diameter of the port is not changed for the injection and by-passing. The flow rate of gas refrigerant passing through the port depends upon its diameter.
Therefore, the diameter of the injection pressure port is set in consideration of a relationship between the injection mass flow of gas refrigerant necessary for an increase in capacity and the by-pass mass flow necessary for a decrease in capacity, and they are not changeable without hingering each other.
In other words, when the passing capacity for an injection pressure gas passing through the injection pressure port is larger than a generating mass flow of an injection pressure gas refrigerant provided by the gas-liquid separator, the gas refrigerant for injection becomes mixed with a liquid refrigerant. If the injection pressure port has a diameter sufficient to permit the aforesaid injection pressure gas to pass at a smaller level than the level of the generating mass flow of gas refrigerant, the problem of mixing the liquid refrigerant will be corrected. On the other hand, the smaller diameter of the injection pressure port increases the resistance against the gas refrigerant by-passed from the pumping chamber toward the suction port side, thereby creating the problem that a desired mass flow of gas refrigerant is not obtainable during by-pass.
In addition, the diameter of the injection pressure port, when made large enough to get the by-pass mass flow necessary for a decrease in capacity, will of course cause a drawing in of the liquid refrigerant during the injection.
The above problems may be solved by forming the diameter of the port large enough to obtain the by-pass mass flow necessary for the decrease in capacity, and providing a resistance passage, such as a capillary tube, at the injection passage channel. This, however, makes the injection passage channel complex in construction and also expensive to produce, whereby this remedy is not satisfactory.
When the compressor is restarted after being stopped, if the high pressure and low pressure at the suction port and discharge port sides are not equalized, an increased starting torque is required for restarting. The restarting generally is carried out after equalizing the pressure.
Since a discharge valve is provided at the discharge port to isolate the suction port side from the discharge port side, the aforesaid pressure equalizing takes time, e.g., about five minutes.
The pressure equalizing generally hastened by a pressure equalizing conduit provided between the high pressure pipe line and the low pressure line and having a solenoid operated openclose valve. The valve is open when operation of the compressor halts.
In the aforesaid refrigeration system, a solenoid valve at the by-pass passage channel is closed and that at the injection passage channel is open to enable the pressure equalizing, requiring a complicated control device for operating the two solenoid valves. On the other hand, the compressor, when starting, can relieve a starting load by a decreasing of capacity for reducing its work load. In this instance, opposite to the pressure equalizing, the solenoid valve at the by-pass passage channel should be open and that at the injection passage channel is closed, thus further complicating the control device.